There are widely employed, as packaging materials for a variety of articles in the fields of foods, pharmaceuticals, electronic part items and the like, bag bodies each equipped on the opening portion with a plastic zipper composed of a pair of male and female hooks on a surface of a plastic film. In particular, there are widely employed plastic zippers each equipped with a slider which is used for opening and closing the zippers because of easiness in opening and closing operations.
This slider is composed of an outside guide and an inside guide. The slider usually employed has a structure that the inside guide is inserted between the male and the female hooks and causes the male/female hooks to disengage, while the outside guide causes the male/female hooks to engage {refer to Japanese Patent Application Laid-Open No. 214920/1996 (Heisei 8)}.
Since in the slider of the conventional structure, the inside guide is inserted between the hooks of a zipper, even if the zipper is completely bound tight, the content in a bag leaks through a gap between the hooks and the inside guide which is inserted between the hooks. Hence, the above-mentioned zipper is unusable for applications requiring hermetical sealing and is for applications not requiring hermetical sealing such as general cargoes.
On the other hand, there is proposed a zipper having such a structure that hermetical sealing can be maintained in a state of a bag being closed with a slider by the use of a specially shaped plastic zipper and a slider adapted thereto (for instance, U.S. Pat. Nos. 5,067,208 and 5,664,299).
In the plastic zippers as disclosed therein, hermetical sealability is maintained by taking advantage of the elasticity of the plastic material which constitutes the zipper for the purpose of facilitating the disengagement even with a weak force, and therefore when the elasticity thereof varies with a variation in temperature or the like, there is caused a fear of incapability of maintaining the hermetical sealability after opening and closing operations, whereby the amount of leakage is increased. Such being the case, the above-proposed zippers are unusable for packaging such content as liquid and the like in which occurrence of leakage is forbidden.
The present inventor previously proposed a hermetically sealable plastic zipper that formed male hooks and female hooks of the zipper on the surface of a plastic, forming a continuous tightening wall parallel to the male hooks on the inside thereof, and further that formed a continuous pressing rib parallel to the female hooks on the inside thereof, so that the zipper is imparted with excellent properties in persistent hermetical-sealability and also impact resistance by the tight contact between the continuous tightening wall and the continuous pressing rib as well as self-tightening effect thereof (Japanese Patent Registration No. 2,938,784). The hermetically sealable plastic zipper is excellent in hermetical sealability and impact resistance and almost free from performance variation due to temperature variation, and accordingly is well suited for packaging liquid and the like.
In addition, the present inventor previously proposed a slider shown in Japanese Patent Application Laid-Open No. 130594/2001 (Heisei 13) which was adapted to the aforesaid hermetically sealable plastic zipper and which does not impair the hermetical sealability thereof, and a plastic zipper equipped with the above-mentioned slider. The constitution thereof is illustrated on FIG. 10, in which protrusions G2-1, G1-2 each serving as a guide for the slider are installed on the opening portion side flange portion (extension portion) of an opening side hook so that the protrusions are parallel to the slider, and also an inside guide S-1 is installed on the plate portion C of the slider S so that the inside guide is positioned between the protrusions and the hooks on the side of the opening portion of the zipper, so as to enable the hermetically sealable plastic zipper to be opened and closed by sliding the slider S as illustrated on FIG. 12 and FIG. 13.
However, the plastic zipper equipped with the slider and a bag body equipped with the zipper suffer from the disadvantage in that unwanted unsealing is unpreventable, since the plastic zipper in a closed state can readily be opened by pulling the protrusions G2-1, G2-2 with the slider S from the outside of the zipper.
The slider of such a constitution that enables unwanted unsealing even after being closed involves a fear of causing contamination with foreign matters or abnormal quality due to unwanted unsealing. Thus in order to eliminate the disadvantage, the present inventor previously proposed a plastic zipper which was equipped with a slider and which was capable of performing completely sealed packaging with a zipper alone and of detecting that unsealing had been made after the sealed packaging, and a bag body equipped with the zipper {refer to Japanese Patent Application Laid-Open No. 345057/2000 (Heisei 12)}.
As exemplified on FIG. 14 through 17, the plastic zipper which is equipped with a slider and a means for detecting unwanted unsealing and a bag body equipped with the zipper each comprise a pair of a male hook and a female hook formed on a plastic surface, have a continuous tightening wall 1-2 and a continuous pressing rib 1-4 that are parallel to the male hooks 1-1 on the inside thereof, and are equipped with a means for bonding the surfaces of the continuous tightening wall 1-2 and the continuous pressing rib 1-4 with easily peelable plastic layers A-1, B-1 in a state of the zipper being engaged and a means for bonding the protrusions G2-1, G2-2 each serving as a guide for the slider that are formed parallel to a pair of male and female hooks 5-1, 5-2 on the plastic surfaces with easily peelable plastic layers A-8, B-8 in a state of the zipper being engaged.
The above-mentioned means are capable of easily opening and closing the zipper by means of the slider as disclosed in the aforesaid Japanese Patent Application Laid-Open No. 130594/2001 after the easily peelable plastic layers are peeled off. However, in order to steadily carry out the peeling of the easily peelable plastic layers with the aforesaid slider, the opening force of the slider needs to be greatly increased by reason of unstable peeling force of the easily peelable plastic layers. Hence, the protrusions serving as a guide for the slider and the inside guide for the slider must be large-sized, thus bringing up the problem that the slider is unusable for a small bag.
Japanese Patent Registration No. 3,026,839 describes a method for opening and closing the zipper fitted with a rib on the end portion of a flange attached to the opening side of the zipper by the use of a slider having a vertical lower side wall portion and a member in inverse U shape. The method, although being easy to obtain the opening force, is required to enlarge the member in inverse U shape inside the slider, when applied to the hermetically sealable zipper which is disclosed in the aforesaid Japanese Patent Registration No. 2,938,784 relating to the proposal of the present inventor and which is excellent in hermetical sealability and the like. Consequently the method is inapplicable to a small bag.
The present inventor proposed a plastic zipper equipped with a slider and imparted with a means for preventing unwanted unsealing, in which the plastic zipper is equipped with a slider and a pair of male and female hooks for sealing formed on plastic surfaces, and is fitted with a pair of male and female hooks for guiding the slider parallel to the hooks for sealing on the opening side, and the inside guide for the slider is positioned between the hooks for sealing and the hooks for guiding the slider {Japanese Patent Application Laid-Open No. 375501/2000 (Heisei 12)}.
The constitution of the aforesaid plastic zipper is such that the hooks for guiding the slider are firstly opened, and the hooks for sealing are opened by catching the inside guide for the slider on the hooks for guiding the slider thus opened. It is possible to simultaneously use these inventions, that is, to install a pair of male and female hooks for guiding the slider parallel to the hooks for sealing on the opening side of the plastic zipper in which the surfaces of the above-mentioned continuous tightening wall and continuous pressing rib are bonded with easily peelable plastic layers. Nevertheless, as is the case with the slider mentioned before, the slider just mentioned involves the problem of being inapplicable to a small bag. Under such circumstances, the development of a plastic zipper equipped with a slider capable of markedly increasing an opening force in spite of its being miniaturized has eagerly been desired.